Length weight from DATRAS

[colinpmillar]

split from:
Problem with HL and CA data #5

many surveys in North America report and analyzes
survey catch rates in units weight per area. However, Datras doesn't
appear to report weight for each specimen in the getHLdata output. If
this were available, FishData (or icesDatras) could sum across
specimens weights in each tow to get total weight by species per tow, for
comparison with N American data.

Would someone at ICES be willing to work with me to make automated code
that uses weight-length relationships to convert specimen length to weight?

jim

[colinpmillar]

hi @James-Thorson - i moved your issue here, are you still interested in working with someone at ICES on this?

[James-Thorson]

Colin,

I took a stab at this previously in FishData (https://github.com/James-Thorson/FishData), but someone recently reported that it broke due to some refactoring of the icesDatras package, which is a dependency. My new job as program lead for HEPR at AFSC doesn't permit me to explore these topics in any detail any more, but I'd be happy to do accept a pull request for suggested changes at FishData, or preferably change FishData to to simply use a new dependency package that sits on top of icesDatras and which does the necessary post-processing to output predicted biomass per sample given data downloaded using icesDatras.

Sorry that I can't volunteer to explore the topic in any detail right now.

Jim

[einarhjorleifsson]

is this approach something along the line you are looking for: https://heima.hafro.is/~einarhj/datrasdoodle/alk.html#converting-abundance-to-weight
e

[colinpmillar]

Thanks Einar – that’s an excellent resource! Thanks for sharing! From: Einar Hjorleifsson <notifications@github.com> Sent: 26 August 2019 23:02 To: ices-tools-prod/icesDatras <icesDatras@noreply.github.com> Cc: Colin Millar <colin.millar@ices.dk>; Author <author@noreply.github.com> Subject: Re: [ices-tools-prod/icesDatras] Length weight from DATRAS (#26) is this approach something along the line you are looking for: https://heima.hafro.is/~einarhj/datrasdoodle/alk.html#converting-abundance-to-weight e — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub<#26?email_source=notifications&email_token=AALO5AFLSDHXEAV6QWD27FTQGRAFZA5CNFSM4G4KMCEKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD5FVOZQ#issuecomment-525031270>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AALO5AD3LHP2WQAEWUDK4ZLQGRAFZANCNFSM4G4KMCEA>.

[einarhjorleifsson]

on the resource, link to the source is: https://github.com/einarhjorleifsson/datrasdoodle
kind of dormant at the moment (last git ~1year old). tried to get more people involved in the writing, but to no avail. partly because people using datras data may not be interested in the tidyverse. me, myself, i may though get back to adding more doodles at some later point in time.
mind you, for species where one does not have length-weights measurements (residing in the ca-data) one could resort to the default newton law of the l-w relationship (w = 0.01 * l^3). sort of as a first approximation, to be then refined by others who have the knowledge / data / strong opinions about what it really should be.
e

[einarhjorleifsson]

If the objective is only to obtain "... total weight by species per tow, ..." we already have icesDatras::getCatchWgt
The (minor) problem is that the unit values returned in that function depends on HH:DataType and HH:HaulDur.
Ergo: Only minor code tweaking is needed to get either or both "per tow" value and "per standardized effort time unit" value.
e